Method of manufacturing formed articles, equipment for practicing same, and formed articles manufactured by the method

ABSTRACT

A thin sheet having a low rigidity is drawn while being depressed over the radiused corner of a die by elastic force or hydrostatic force to obtain a formed article whose sidewall part and flange part have no wrinkles. The force is applied through an annular rigid body on which elastic is exerted. The hardness of the rubber is preferably approximately 70 to 85 in accordance with ASTM D 2240 Durometer A. A laminate not more than about 200 μm in thickness and consisting of a thermoplastic resin film, aluminum foil and a heat-sealable resin film is drawn into a formed article or a container which is light in weight and suitable for containing foods, for instance.

This is a division of application Ser. No. 921,162 filed July 3, 1978,and now U.S. Pat. No. 4,225,553.

BACKGROUND OF THE INVENTION

This invention relates to a method of drawing a metal foil or sheet, orplastic film or sheet, or their laminate into formed articles, andequipment for practicing same and formed articles manufactured by themethod. The present invention is directed more particularly to a methodof drawing a metal foil or sheet, or a plastic film or sheet, or theirlaminate which is of the order of 7 to 200 μm in thickness and has arelatively low rigidity, into a formed article which has no wrinkles,and equipment for practicing same and formed articles manufactured bythe method.

Containers extremely thin in wall thickness which are made of a metalfoil or sheet such as aluminum foil or tin plate, or a plastic film orsheet, or their laminates, are extensively employed for packaging goodsor medicines and so on. However, such containers have scarcely beenformed by drawing. This is due to the following reasons: These foil,sheet, film and laminate, namely, blanks are less in rigidity.Accordingly, if the blanks are drawn by the ordinary drawing method,wrinkles are significantly created on the formed article or container orshell at the radiused corner of the die and are distributedsubstantially entirely over the flange and the sidewall portion of theshell. This will undoubtedly defile the appearance of the containers. Inaddition, it is impossible to hermetically seal the containers withtheir flange portions by lids so as to prevent leakage of the contentsand deterioration of the contents due to entry of air and moisture.

In order to overcome this difficulty, a method is extensively employedin which, after heat-softened, a plastic film or sheet, or a compositefilm or sheet consisting of plastic materials is subjected topressurized air forming or vacuum forming to produce a formed article.This method is a so-called bulging method which can be applied only toplastic films or sheets which extend 100% to 200% or more atheat-softened state. Accordingly, this method is disadvantageous in thata step of heating is required, and unlike drawing, it is impossible tosubject the blank to cold forming which is carried out at roomtemperature or a temperature around the room temperature. It goeswithout saying that this method cannot be applicable to aluminum foil ortin foil.

In the case where containers are made of plastic only, it has been foundthat it is rather difficult to attain complete barrier for oxygen ormoisture, that is, such containers are not suitable in the field ofpackaging foods to be preserved for a long time at room temperaturewhere sophisticated technique is required. In order to eliminate thisdrawback, a laminate of aluminum foil, or the like, and plastic films orsheets has been provided recently. In this case, in view of materialsaving and cost reduction, the aluminum foil should be as thin aspossible, but to the extent that the contents in the container isprevented from inroading of oxygen and moisture. Accordingly, laminatesmade of a thin aluminum foil 7 to 30 μm in thickness and polyester,polyethylene, polypropylene, nylon or polycarbonate films etc. severalto several tens of μm in thickness have been provided to package foodsor the like. However, since the laminate of this type contains aluminumfoil, the elongation thereof is no more than several to 50%, andtherefore manufacturing a formed article from the laminate in accordancewith the above-described pressurized air or vacuum forming ispractically impossible. Accordingly, such laminates are used mainly formanufacturing pouches.

In a drawing method, unlike a bulging method, the thickness of a blanksheet is scarcely changed during drawing, and the elongation of theblank needs not to be so high. Accordingly, in the drawing method, it ispossible to obtain a formed article such as a cup by subjecting theaforementioned very thin metal foil or sheet, or a plastic film or sheetor laminates thereof to cold-drawing. However, in this conventionaldrawing, wrinkles are remarkably created on the formed article at theradiused corner of the die, and therefore heretofore it is impossible tomanufacture formed articles which can be commercialized.

In other words, in the conventional drawing, when a blank is drawn intothe die by the punch, the blank has a portion which is not restrained onthe radiused corner of the die. However, in the case where the blank issufficiently thicker than 200 μm and especially it is a metal sheet, therigidity of the blank is considerably high, so that wrinkles arescarcely created on the formed article at the radiused corner. On thecontrary, the rigidity of a plastic laminate thinner than 200 μmincluding a thin aluminum foil 7 to 30 μm is relatively low, andtherefore if this plastic laminate is drawn in accordance with theconventional method, wrinkles will be necessarily created.

SUMMARY OF THE INVENTION

In view of the foregoing, a primary object of this invention is toprovide a drawing method in which creation of wrinkles on a formedarticle at the radiused corner of the die is prevented.

A further object of the invention is to provide a drawing equipment inwhich a thin sheet having a relatively low rigidity can be drawn withoutcreating wrinkles on a formed article at the radiused corner of the die.

A still further object of the invention is to provide a formed articlefine in appearance without wrinkles which is obtained by drawing a metalfoil or sheet, or a plastic film or sheet, or their laminate about 7 to200 μm in thickness.

A specific object of the invention is to provide a formed article finein appearance without wrinkles which is obtained by drawing a laminateconsisting of a metal foil of about 7 to 30 μm and plastic films ofseveral to about one hundred of μm in thickness.

In this invention, a force for resisting creation of wrinkles on a blanklow in rigidity being drawn, that is, elastic force or hydrostatic isapplied to the blank at the radiused corner of the die substantiallythroughout the drawing operation, thereby to provide a formed articlehaving no wrinkles.

The novel features which are considered characteristic of this inventionare set forth in the appended claims. This invention itself, however, aswell as other objects and advantages thereof will be best understood byreference to the following detailed description of illustrativeembodiment when read in conjunction with the accompanying drawings, inwhich like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a sectional view for a description of a conventional drawingmethod; and

FIGS. 2 and 3 are sectional views showing an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an explanatory diagram for a description of a conventionaldrawing method. Referring to FIG. 1, a punch 2 is fixedly secured to abolster 1, and a blank holder 3 is connected to the bolster 1 through acushioning means 4 which utilizes a spring, pneumatic pressure or liquidpressure. A die 5 is affixed to a ram 6. In FIG. 1, the bolster and theram are arranged above and below, respectively; however, the arrangementof them may be reversed. This can be applied to FIGS. 2 and 3. A blankto be drawn, or a thin sheet 7 (hereinafter referred to as "a workpiece7" when applicable) is clamped between the blank holder 3 and the die 5under a suitable pressure, and is then drawn as the punch enters thedie. In this drawing operation, no force is exerted on a portion of thesheet 7, which lies on the radiused corner 8 of the die 5, by the blankholder 3, and therefore the portion is in a so-called free state untilthe punch 2 is brought into contact therewith. Consequently, wrinkleswill be produced on the portion by circumferential compressive force, ifthe sheet is a thin one having a low bending rigidity.

In this invention, the above-described difficulty is eliminated by usinga drawing machine described below, and particularly a punch describedbelow in the drawing machine. That is, the drawing machine comprises apunch and a die having a cavity corresponding to the punch, so that athin sheet is drawn into the cavity of the die by the punch thereby toform a formed article.

Shown in FIG. 2 is an embodiment of this invention in which anadditional means for restraining a work-piece at the radiused corner ofa die is employed.

The drawing machine shown in FIG. 2 comprises a punch, and a die havinga cavity corresponding to the punch, so that a thin sheet having arelatively low rigidity is drawn into the cavity of the die to form aformed article or a shell. This drawing machine further comprises adepressing member in the form of an annular rigid body, is movablyplaced around the punch. In a drawing operation, the depressing memberis brought into contact with the surface of the sheet, which is oppositeto a face of the sheet which is brought into contact with the radiusedcorner of the die, so that the sheet is depressed over the radiusedcorner of the die by the elastic or hydraulic force through thedepressing member substantially throughout the drawing. In thisembodiment, an ordinary punch 2 is employed and in addition to a blankholder 3', the depressing member 11 is connected through a cushioningmember 12 such as springs, pneumatic or hydraulic pressure devices to abolster 1 so as to prevent creation of wrinkles on work-pieces.

The depressing member 11 operates to slide along the outer wall of thepunch 2. The outside diameter of the depressing member 11 issubstantially equal to the diameter of a circle 8a which is formed bythe intersecting line of the die radiused corner 8 and the upper planeof the die. The lower end surface 11a of the depressing member 11 is soformed as to substantially conform to the shape of the die radiusedcorner 8 so that the elastic or hydraulic pressure is uniformly appliedto the die radiused corner 8.

In drawing operation, first only the punch 2 depresses the work-piece 7.As soon as the work-piece 7 is brought into contact with the entire dieradiused corner 8, the cushioning member 12 is operated to move thedepressing member 11. As a result, the lower end surface 11a of thedepressing member 11 depresses the upper surface, as viewed in the FIG.3, of the portion of the work-piece which is in contact with the dieradiused corner 8. This depression is carried out until the drawing iscompleted.

FIG. 3 shows a state of the work-piece which has been drawn by thedrawing machine. The pressure generated by the cushioning member 12 isapplied through the depressing corner 11 to the work-piece to preventcreation of wrinkles thereon.

The invention has been described with the particular embodiment:however, it should be noted that the invention is not limited thereto orthereby. A blank, such as a metal foil or thin sheet, to be employedaccording to the present invention may be iron, steel, copper and nickelsheets or tin plate, or sheets made of alloys of these materials, orsuch sheets coated with lacquers or subjected to surface treatment. Ablank, such as a plastic film or sheet, to be employed in this inventionmay be polypropylene, nylon and polycarbonate sheets or their laminates.Polyester or polycarbonate sheets can be solely drawn because they canbe subjected to cold forming.

The method and equipment according to the invention is most applicableto a film laminate less than about 200 μm which consists of an aluminumfoil about 7-30 μm in thickness and plastic films covering the twosurfaces of the aluminum foil.

If the surface of the laminate which is brought into contact with thepunch during the drawing operation, that is, the layer of the laminatewhich is the inner surface of the formed article is of heat-sealableresin, a sealed container light in weight can be obtained with its lidheat sealed. This container can be subjected to retort sterilization,and, therefore, it is suitable as a container for foods, beverages andthe like which can be preserved at room temperature. The heat-sealableresin may be polyolefins such as polyethylene and polypropylene, ornylon 11 or nylon 12 or polyester ether resin or their copolymers andblends, for instance.

The plastic film of the laminate which is brought into contact with thedie serves to protect the intermediate layer or the aluminum foil fromcorrosion, to improve lubrication in drawing, and to maintain theconfiguration of a formed article.

Plastics preferable for this purpose are oriented or non-orientedpolyethylene terephthalate, polyimid resin, polypropylene,polycarbonate, and their copolymers and blends, and furthermore othercold-formable synthetic resins.

The term "foil" or "film" as used herein is, in general, intended tomean a foil or film thinner than 100 μm, and the term "sheet" means asheet thicker than 100 μm. The present invention is most suitable fordrawing a thin work-piece having relatively low rigidity whose thicknessis less than about 200 μm. An indicated in Table 2, the presentinvention is sufficiently applicable to sheets ranged from 20 μm toabout 200 μm in thickness.

The embodiment of the invention has been described with reference tonormal drawing. However, it should be noted that the invention can beapplied to deep-drawing as well as drawing-bulging in which the bottomof a formed article is subjected to bulging, to the extent that thearticle is not broken.

The method and equipment according to the invention can draw a thinsheet into various configurations of the sidewall section such ascircle, ellipse, corner-rounded triangle, rectangle, hexagon, andcorner-rounded polygon.

The forming temperature is not always limited to room temperature; thatis, it may be higher than room temperature where required, if it doesnot damage a work piece and the elastic wall such as rubber employed forthe punch.

As is apparent from the above description, according to the inventionwork-pieces such as metal foils or sheets or plastic films or sheets ortheir laminates which are relatively low in rigidity can be drawn intobeautiful shells such as containers without wrinkles, althoughproduction of such articles has been impossible by the conventionalmethod. Since the container produced according to the invention has nowrinkles, the container can be hermetically sealed with its flange andthe lid. Accordingly, the containers are most suitable for cooked foodsor medicines and so forth which should preserved for a long time at roomtemperature and should be prevented from inroading of oxygen andmoisture.

What is claimed is:
 1. A drawing machine comprising:a punch, and a diehaving a cavity formed therein corresponding to said punch and having aradiused corner, said punch for drawing a thin sheet having a relativelylow rigidity into said cavity in said die to manufacture a formedarticle, and means comprising a depressing member having an end surfaceof the depressing member being formed substantially conforming to theshape of the radiused corner which is disposed movable around said punchin such a manner that said end surface of said depressing member isbrought to cooperate with said radiused corner with said thin sheettherebetween into contact with a surface of said thin sheet which isopposite to a face of said thin sheet which is brought into contact withthe radiused corner of said die and said sheet is depressed by saiddepressing member substantially throughout the drawing.
 2. The drawingmachine as claimed in claim 1, in which said depressing member is anannular rigid body.
 3. The drawing machine according to claim 1, furthercomprising:a blank holder means for operatively holding edges of saidsheet against said die during the drawing.
 4. The drawing machineaccording to claim 3, further comprising:a bolster, said punch isconnected rigidly to said bolster, cushioning means connects said blankholder means to said bolster.
 5. The drawing machine according to claim3, wherein:said blank holder means is for holding said edges of saidsheet initially before the drawing as well as during the drawing.
 6. Thedrawing machine according to claim 5, whereinsaid blank holder meansfurther for permitting slipping of said edges during the drawing.
 7. Thedrawing machine according to claim 1, wherein:said end surface is alower surface of said depressing member defining an annular,substantially radially outwardly and downwardly facing concave surfacesubstantially complementary to said radiused corner of said die.
 8. Thedrawing machine according to claim 7, wherein:said depressing member hasan outside diameter substantially equal to the diameter of a circleformed by an intersecting line of the radiused corner of the die and anupper plane of the die.
 9. The drawing machine according to claim 1,wherein:said depressing member has a lowermost end which is alwayshigher than a lowermost end of said punch.
 10. The drawing machineaccording to claim 1, further comprising:cushioning means for connectingsaid depressing member movably relative to said punch.
 11. The drawingmachine according to claim 10, further comprising:a bolster, said punchis connected rigidly to said bolster, said cushioning means is connectedto said bolster.